Templates and automations based on states() break when unit of measurement is changed #145100
Description
The problem
After changing the unit of measurement on several time-based sensors (e.g., from seconds to minutes), I started encountering inconsistent behavior across automations and templates. One example is a Jinja template used in a push notification message:
{{ (states('sensor.ups_battery_runtime') | int) | timestamp_custom('%H:%M:%S', local = false) }}
Originally, this returned 00:54:00 (seconds). After the unit was changed to minutes, it returned 00:00:54, causing a misleading notification (54 seconds instead of 54 minutes). This silent behavioral change led to other issues as well, such as with utility meters (see my other report here).
I now feel completely lost, as I have no easy way to check which of my automations and templates (among hundreds) were affected by my seemingly harmless unit changes. I thought I'd just make the times presented in the UI more human readable (e.g. 1,5 hour rather than 5400 seconds ;)), but in fact I caused all dependencies like automations and templates to change their behavior silently, and I don't even know which ones are broken now. I'm just noticing now and then some strange behaviors like the one I'm describing now.
To improve robustness and prevent such breakages, please consider allowing templates to read sensor state in a fixed unit, e.g.:
{{ (states('sensor.ups_battery_runtime', unit='s') | int) | timestamp_custom('%H:%M:%S', local = false) }}.
This would make template logic predictable and resilient even if an entity's unit is later changed in the UI.
Please, let me know if this suggestion makes sense or if this should just be approached differently. I appreciate it, thanks!
What version of Home Assistant Core has the issue?
2025.5.1
What was the last working version of Home Assistant Core?
No response
What type of installation are you running?
Home Assistant OS
Integration causing the issue
No response
Link to integration documentation on our website
No response
Diagnostics information
No response
Example YAML snippet
{{ (states('sensor.ups_battery_runtime') | int) | timestamp_custom('%H:%M:%S', local = false) }}Anything in the logs that might be useful for us?
Additional information
An argument that would allow specifying the unit would make your logic based on the sensor's value reliable: states('sensor.ups_battery_runtime', unit='s')